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Re: Aquatic Plants Digest V2 #1010

> Date: Sun, 12 Oct 1997 09:40:05 -0400
> From: "Frank I. Reiter" <FIR at istar_ca>
> Subject: Transformers for Dupla heating cables
> > Date: Sat, 11 Oct 97 21:56:36 -0700
> > From: gomberg at wcf_com
> >
> > On 10/11/97 at 03:48 p, Jean (Aquatic Plants Digest) said:
> >
> > >To try this, attach the PRIMARIES of the two transformers in
> > >PARALLEL, attach the secondaries of TWO transformers in series,
> > >then check the resultant voltage.
> >
> >
> > This is very hazardous.  Most inexpensive transformers do not have
> > secondaries that are isolated from the primaries (transformers that
> > do are called isolation transformers).  Connect the secondaries
> > together at all may be dangerous.

Hmmm.  I thought this was a pretty common  way of connecting transformers.

> Could you elaborate?  I have been told by several local transformer 
> suppliers that connecting two lower powered transformers in series "Will 
> not work" but I do not understand the problem. 

Most of the Electronics Shop Guy's I've dealt with know little beyond the 
most basic application of a part.  If you go beyond that you often can't 
trust their input.

> As I understand 
> transformers, current in the secondary comes from the magnetic field of the 
> primary and there is no electrical path between the two.  What is the 
> difference between a regular transformer and an isolation transformer?

That is my understanding as well.

> What consequence does one risk when connecting transformer secondaries in 
> series?

A potential problem is that the secondary has to be rated to handle twice
as much current as it would need to be if it were standing alone in the
same circuit.  Be careful that the secondary has an adequate current

Roger Miller